Glass fiber mat has long been manufactured by directing continuous strands of glass fiber down onto a moving conveyer as the fiber trajectory and point of impingement is oscillated back and forth across the width of the conveyor. This builds up a random, homogeneous layer of interengaging strands in a swirled, overlapping arrangement. A variety of methods and apparatus for directing the glass fiber onto the moving conveyer have been attempted in the past several decades.
For example, U.S. Pat. No. 2,855,634 illustrates a plurality of continuous glass fiber strands directed onto a conveyer from a plurality of different pulling wheels distributed above the conveyer.
Others have suggested the deflection of a continuous glass fiber which is impinged upon a reflecting surface. Such patents include U.S. Pat. Nos. 2,736,676 and 4,345,927.
A more practical system for oscillating the trajectory of the glass strands utilizes a pulling wheel, having lateral slots through which the fingers of a finger wheel project. The finger wheel rotates about an axis of rotation which is offset from the axis of rotation of the pulling wheel. The fingers move out to release the strand from the pulling wheel so that it is projected along a substantially tangential path from the wheel to the moving conveyer. Structures of this type include those shown in U.S. Pat. Nos. 4,368,232 and 3,485,610.
Another system utilizes air blasts in place of the fingers, such as is illustrated in U.S. Pat. No. 2,450,916. The linear feed of a continuous multi-filament strand is illustrated in U.S. Pat. No. 2,935,179.
Finally, more recently, oscillating air current systems have been used for guiding a glass fiber along its trajectory and to cause the trajectory to oscillate back and forth laterally across the conveyer. Such systems are illustrated in U.S. Pat. Nos. 2,859,506; 2,875,503; 3,738,894; and 4,601,741.
One of the principal goals of a system for producing glass fiber mat is to fabricate a product exhibiting a uniform distribution of fibers randomly across the conveyer within the limits of the width of the finished glass fiber mat. Ideally, such a mat has a uniform density laterally from one edge, through the center, to the other edge of the mat and would terminate with relatively sharp lateral edges.
One difficulty with the air current systems is that the fibers flutter uncontrollably, providing little control of the curl and providing relatively ragged edges of nonhomogeneous density. Thus, the mat product is not sufficiently uniform near its edges. This necessitates that the mat be manufactured with an oversized width so that a strip of material can be removed from the opposite, lateral Substantial trim loss scrap is therefore produced.
A difficulty with the finger wheel systems is that the fingers create a small kink in each fiber and no control of the curl is permitted.
It is therefore an object and feature of the present invention to provide an apparatus and method which permits more accurate control of the glass fiber which is projected onto the conveyer without the inaccuracies caused by turbulent air currents or the deformities caused by the finger wheels.
A further object and feature of the present invention is to provide improved uniformity and density across the width of the glass fiber mat and also provide for control of the curl.